Hydrocarbon oil compositions typically comprise a mixture of at least one hydrocarbon base oil and one or more additives, where each additive is employed for the purpose of improving the performance and properties of the base oil in its intended application; e.g., as a lubricating oil, heating oil, diesel oil, middle distillate fuel oil, and so forth. Lubricating oil compositions face rather stringent viscosity requirements, as set, for example, by ASTM specifications. Such compositions must meet a minmum viscosity requirement at high temperature (i.e., at least about 100.degree. C.) and a maximum viscosity requirement at low temperature (about -5 to -30.degree. C.). The minimum viscosity requirement at high temperature is intended to prevent the oil from thinning during engine operation to the point at which excessive engine wear and increased oil consumption would result. The maximum viscosity requirement at low temperature facilitates engine start-up in cold weather and also ensures the cold oil has sufficient pumpability and flowability to avoid engine damage due to insufficient lubrication.
In formulating a lubricating oil composition which meets both the low and the high temperature viscosity requirements, a formulator can use a single lubricating base oil of desired viscosity or a blend of oils of different viscosities, and he can manipulate the kinds and amounts of additives that must be present to achieve not only the viscosity requirements, but also requirements specified for other properties, such as dispersancy, pour point and cloud point. Generally, the mere blending of oils having different viscosity characteristics does not enable the formulator to meet the low and high temperature viscosity requirements of lubricating oil compositions. Instead, the primary tool for meeting the requirements is the use of viscosity index improving additives, hereinafter referred to as viscosity index improvers or, more simply, VI improvers.
A VI improver is conventionally an oil-soluble long chain polymer, often a hydrocarbon-based polymer with a number average molecular weight in the range of 20,000 to 200,000. The large size of these polymers enables them to significantly increase kinematic viscosities of base oils even at low concentrations. Unfortunately, lubricating oil solutions containing these VI improvers are non-Newtonian in nature. As a result, these solutions tend to give lower viscosities than expected in a high shear environment, such as that found in an operating internal combustion engine. It is believed that this behavior arises from shear-induced alignment of the VI polymer chains. Consequently, the VI improvers increase the low temperature viscosity of a lubricating base oil to a greater extent than they increase its high temperature viscosity. As a result, the two viscosity requirements for a lubricating oil composition become increasingly antagonistic as increasingly higher levels of VI improver are employed. Eventually, a point can be reached where the amount of VI improver added to achieve the required minimum viscosity at high temperature precludes the possibility of meeting the required maximum viscosity at low temperature. Accordingly, constraints exist on the amount of VI improver which a formulator can employ for a given lubricating base oil or base oil blend to meet the low and high temperature viscosity requirements for the lubricating oil composition.
The task of formulating a lubricating oil composition is more complicated than merely selecting the appropriate kind and amount of VI improver to add to the base oil. In addition to VI improvers, lubricating oil compositions typically contain dispersant additives, which can also affect the viscosity characteristics of the composition. Dispersants are typically polymeric materials with an oleophilic component providing oil solubility and a polar component providing dispersancy. Dispersants generally have a number average molecular weight of about 10,000 or less, and, consequently, have polymer chains much smaller than those of a typical VI improver. Among the materials which have been employed as dispersants are hydrocarbon polymers modified to contain nitrogen- and ester-based groups. Polyisobutylene is perhaps the hydrocarbon polymer most commonly used in the preparation of dispersants, although other hydrocarbon polymers, such as ethylene-.alpha.-olefin copolymers, can be employed as well. The primary function of a dispersant is to maintain in a suspension in the oil any insolubles formed by oxidation, etc. during use, thereby preventing sludge flocculation and precipitation. The amount of dispersant employed is dictated and controlled by the effectiveness of the particular material in achieving its dispersant function. Motor oils commercially available at U.S. service stations typically contain about four times as much dispersant as VI improver, based on active ingredient.
Conventional dispersants can also increase the low and high temperature viscosity characteristics of a base oil by virtue of their polymeric nature. However, because dispersant polymer molecules are much smaller than those of a VI improver, the dispersant is much less shear sensitive. As a result, a dispersant contributes more to the low temperature viscosity of the lubricating oil relative to its contribution to the high temperature viscosity than does a VI improver. Moreover, the dispersant, with its shorter polymer chains, contributes much less to the high temperature viscosity of the base oil in an absolute sense than does the VI improver. Thus, the magnitude of the low temperature viscosity increase induced by the dispersant can exceed the low temperature viscosity increase induced by the VI improver without the benefit of a proportionately greater increase in high temperature viscosity as obtained from a VI improver. Consequently, as the dispersant-induced low temperature viscosity increase causes the low temperature viscosity of the oil to approach the maximum viscosity permitted at low temperature, it becomes increasingly difficult to introduce an amount of VI improver sufficient to meet the minimum viscosity required at high temperature without crossing the low temperature viscosity threshold.
A lubricating oil composition formulated with a kind and amount of dispersant and VI improver sufficient to meet the low and high temperature viscosity requirements and still achieve effective dispersancy does not necessarily end the formulator's task. The lubricating oil composition must meet other performance criteria, such as pour point and cloud point, which may necessitate the employment of still other additives.
Cloud point (ASTM D2500) is the temperature at which wax crystals first appear as a haze in a hydrocarbon oil upon cooling. These wax crystals typically have the highest molecular weight of the waxes in the hydrocarbon oil and, therefore, the lowest solubility. The cloud point of a hydrocarbon oil reflects the temperature at which problems in filtering the oil are encountered. However, the cloud point of a lubricating oil (as against a fuel oil) is of less significance than is its pour point, because the filters typically encountered by a lubricating oil (e.g., oil filters for internal combustion engines) have a relatively large pore size, and filter plugging is less of a problem.
Pour point is the lowest temperature at which a hydrocarbon oil will pour or flow when chilled without being disturbed under specified conditions. As the hydrocarbon oil is chilled, wax in the oil precipitates into crystals which form a network. The pour point of the oil is marked by the temperature at which the fluid component of the oil is immobilized by the wax crystal network. See, e.g., Mark, Herman, editor, Encyclopedia of Polymer Science and Engineering, vol. 11, John Wiley & Sons, New York, 1988, pg. 26-27. The lubrication of an engine or other equipment at temperatures near and below the pour point is significantly impaired, because the distribution of the chilled oil by pumping or siphoning is difficult or impossible. Operation of the engine or other equipment under such conditions will quickly result in significant damage and ultimately failure.
Because the waxes contributing to low-temperature problems are present in essentially all non-synthetic hydrocarbon oils used today, various additives have been developed to beneficially influence the oils' low temperature flow properties. These additives are generically referred to as lubricating oil flow improvers (LOFI's) or pour point depressants. The LOFI's act to modify the size, number, and growth of wax crystals in chilled lubricating oils in a manner imparting improved handling, pumpability, and/or vehicle operability at low temperatures.
The majority of LOFI's are or contain polymers of one of two general types--backbone polymers and side-chain polymers. The backbone polymers, such as ethylene-vinyl acetate (EVA) copolymers, have various lengths of methylene segments randomly distributed in the backbone of the polymer, which associate or cocrystallize with the wax crystals. Extended wax crystal growth, and the concomitant formation of crystalline wax networks, is inhibited, however, by the branches and non-crystallizable segments in the polymer.
The side-chain polymers, the predominant variety of LOFI's, have methylene segments in their side chains, which are preferably non-branched side chains. These polymers work similarly to the backbone polymers except the side chains have been found to be more effective in inhibiting extended wax crystal growth in isoparaffins as well as the normal paraffins found in lube oils. More specifically, LOFI's are typically derived from unsaturated carboxylic acids or anhydrides which are esterified to provide pendent ester groups derived from a mixture of alcohols. Representative examples of this type of side chain LOFI include dialkyl fumarate-vinyl acetate copolymers and esterified styrene/maleic anhydride copolymers.
Unfortunately for the formulator, the LOFI's and other additives added to control the pour point, etc. of the lubricating oil composition may interact with the VI improver and the dispersant in a manner adversely affecting the composition's viscosity and dispersancy. Conversely, the dispersant and/or VI improver may contribute adversely to the performance of these other additives. Furthermore, even in the absence of other additives, the dispersant and VI improver may interact with the base oil itself to degrade the cloud point, pour point, etc the oil would otherwise have.
As an example, dispersants employing ethylene-.alpha.-olefin copolymers, unlike those based upon polyisobutylene, possess linear methylene segments derived from sequential units of ethylene in the polymer chain. These methylene segments possess the capability of interacting with the waxes present in the lubricating base oil. In some cases these interactions can be harmful to the low temperature properties of the oil and can in certain circumstances counteract and defeat the effect sought to be induced by the LOFI. Thus, dispersants based upon ethylene-.alpha.-olefin copolymer backbones must be carefully selected to avoid adverse wax interactions, while simultaneously achieving the proper overall high and low temperature viscosity requirements of the oil, which may or may not be significantly affected by the wax interaction. Furthermore, these problems must be solved in such a way that the dispersancy of the ethylene-.alpha.-olefin-based dispersant remains acceptable.
As already noted, short-chain hydrocarbon polymers modified to contain certain polar groups, particularly nitrogen- and ester-based groups, have been widely used as ashless dispersant additives in lubricating oils. The nitrogen- and ester-based dispersants can be prepared by first functionalizing the long-chain hydrocarbon polymer with maleic anhydride to form the corresponding polymer substituted with succinic anhydride groups, and then derivatizing the succinic anhydride-substituted polymer with an amine or an alcohol or the like. Polyisobutylene has often been the polymer of choice, chiefly because it is readily available by cationic polymerization from butene streams (e.g., using AlCl.sub.3 catalyst). Such polyisobutylenes generally contain residual unsaturation in amounts of about one ethylenic double bond per polymer chain, positioned along the chain. The ethylenic double bonds serve as sites for functionalizing the polyisobutylenes by, for example, the thermal "ene" reaction (i.e., by direct reaction with maleic anhydride or one or more other dicarboxylic acid moieties).
The polyisobutylene polymers (PIB) employed in most conventional dispersants are based on a hydrocarbon chain of a number average molecular weight (M.sub.n) of from about 900 to 2500. PIB having a M.sub.n of less than about 300 gives rather poor performance results when employed in dispersants because the molecular weight is insufficient to keep the dispersant molecule fully solubilized in lubricating oils. On the other hand, high molecular weight PIB (M.sub.n &gt;3000) becomes so viscous that conventional industrial practices are incapable of handling this product in many operations. This problem becomes much more severe as the PIB molecular weight increases to 5,000 or 10,000.
Increased amounts of terminal ethylenic unsaturation in polyisobutylene (so-called "reactive polyisobutylene") have been achieved by BF.sub.3 -catalyzed polymerization of isobutylene. Exemplary of references disclosing these polymers is U.S. Pat. No. 4,152,499. Nonetheless, the reactive polyisobutylenes can still contain substantial amounts of unsaturation elsewhere along the chain. Furthermore, it is difficult to produce reactive polyisobutylene polymers at molecular weights of greater than about 2,000, and, in any event, the reactive polyisobutylenes still have the above-noted viscosity increase disadvantages as their molecular weights are increased.
A variety of hydrocarbon polymers have been disclosed to be suitable polymer backbones for the preparation of ashless nitrogen and ester dispersants. U.S. Pat. No. 4,234,435, for example, discloses dispersants prepared from polyalkenes with a Mn value of from 1,300 to about 5,000 and M.sub.w /M.sub.n of about 1.5 to about 4. The polyalkenes are homopolymers or interpolymers of polymerizable olefin monomers, usually polymerizable terminal olefin monomers, of 2 to about 16 carbon atoms. The polyalkenes are functionalized by reaction with one or more acidic reactants such as maleic acid, fumaric acid and maleic anhydride. This patent, however, provides no examples directed to the preparation of suitable polyalkene ethylene-.alpha.-olefin interpolymers or their use as dispersant backbones.
It is generally known that ethylene-.alpha.-olefin copolymers can be prepared by polymerizing ethylene and the .alpha.-olefin co-monomer using conventional Ziegler-Natta catalysts (e.g., VCl.sub.4 or VOCl.sub.3 with a halide source, such as organoaluminum halides and/or hydrogen halides). However, because of the relatively high activity of these catalysts, the resulting copolymers tend to have number average molecular weights well in excess of about 10,000 and thus are generally not suitable for use as polymer backbones for dispersants. For example, ethylene-propylene (EP) polymers and ethylene-propylene-diene terpolymers (EPDM) having a viscosity average molecular weight (M.sub.v) of from about 20,000 to 300,000 are produced using Ziegler catalysts. These high molecular weight EP and EPDM polymers find use as viscosity index improvers. See, e.g., U.S. Pat. Nos. 3,563,964; 3,697,429; 4,306,041; 4,540,753; 4,575,574; and 4,666,619. Other high molecular weight olefin polymers produced using Ziegler catalysts, such as polypropylenes and ethylene-1-butene copolymers, have also been disclosed to be useful as viscosity index improvers. See, e.g., U.S. Pat. No. 4,540,756.
It is also known in the art that ethylene-.alpha.-olefin copolymers useful as viscosity index improvers may, when functionalized with acid moieties such as maleic anhydride and subsequently reacted with an amine, be employed as multifunctional viscosity index improvers. See, e.g., U.S. Pat. Nos. 3,316,177; 3,326,804; 4,160,739; 4,161,452; 4,171,273; and 4,517,104.
Certain of the references disclosing the production of ethylene-.alpha.-olefin copolymers using conventional Ziegler catalysts include within their scope the production of copolymers having relatively low molecular weights; i.e., values of M.sub.n below about 10,000. However, these references often disclose the lower molecular weight copolymers to be outside the preferred ranges, and they often do not provide examples of the preparation or use of low molecular weight polymers. U.S. Pat. No. 4,863,623, for example, discloses lubricant additives having viscosity-improving, dispersancy and anti-oxidant properties, prepared from ethylene copolymers and terpolymers of C.sub.3 to C.sub.10 .alpha.-monoolefins and optionally non-conjugated dienes or trienes. To prepare the additive, the copolymer or terpolymer is first grafted with an ethylenically unsaturated carboxylic function, preferably maleic anhydride or a derivative thereof, by the thermal "ene" process or by grafting in solution or in solid form using a radical initiator, and the grafted material is then further derivatized with an amino-aromatic polyamine compound. The ethylene copolymers and terpolymers are disclosed to have a molecular weight ranging from about 5,000 to 500,000 and an .alpha.-olefin content of 20 to 85 mole %. The patent discloses the copolymers and terpolymers can be prepared using Ziegler type catalysts. The preferred molecular weight range is disclosed to be 25,000 to 250,000, and the examples are directed to the use of EP copolymers having an average molecular weight of 80,000.
Along similar lines is Canadian Patent Application 2,021,959. The application discloses dispersant and anti-oxidant lubricant additives prepared from ethylene copolymers and terpolymers of C.sub.3 to C.sub.10 .alpha.-monoolefins and optionally non-conjugated dienes or trienes. As in U.S. Pat. No. 4,863,623 supra, the additive is produced by first thermally or radically grafting the copolymer or terpolymer with an ethylenically unsaturated carboxylic acid material and then reacting the grafted polymer with an amino-aromatic polyamine compound. The ethylene copolymers and terpolymers are disclosed to have a molecular weight ranging from about 1,000 to 40,000. It is further disclosed that the copolymers and terpolymers can be prepared using Ziegler catalysts. But it is also noted that many polymerization processes produce the copolymers and terpolymers with molecular weights substantially above 75,000 thus requiring that the polymers be degraded, usually mechanically or thermally, to obtain polymers in the prescribed M.sub.n range of 1,000 to 40,000. The examples are directed to the grafting of EP copolymers having number average molecular weights higher than 10,000.
Ethylene-.alpha.-olefin copolymers which have sufficiently low molecular weights to be useful dispersant polymer backbones can be prepared using conventional Ziegler-Natta catalysts by conducting the polymerization in the presence of a molecular weight regulator such as hydrogen. A key disadvantage to the use of hydrogen as a chain stopper is that it can result in the saturation of the olefinic double bond content in the copolymers. The resulting low unsaturation content of the copolymers makes their functionalization by a thermal "ene" reaction highly unattractive.
U.K. Patent 1,329,334 exemplifies the use of a conventional Ziegler-Natta catalyst for the preparation of ethylene-.alpha.-olefin copolymers of relatively low molecular weight. The patent discloses the production of ethylene polymer wax by polymerizing ethylene and optionally an .alpha.-olefin in the presence of hydrogen using a catalyst composed of a titanium or vanadium halogen compound supported on a carrier (a hydrocarbon-insoluble Mg compound) and an organo-aluminum compound. The molecular weight and density of the polymer wax are controlled by the amount of hydrogen and/or .alpha.-olefin used in the polymerization. At the temperatures and pressures used in the polymerization, the content of double bonds in the polymer wax is reduced. The polymer wax is disclosed to have a M.sub.v in the range of 400 to 20,000. The wax may be oxidized without the formation of cross-linkages due to the small content of double bonds in the wax, and the oxidized wax may be modified by reaction with a maleic acid compound. The patent contains an example disclosing the production of an ethylene-1-butene polymer wax containing 28 ethyl groups per 1000 carbon atoms, which is equivalent to about 94 mole % ethylene assuming the ethyl groups in the polymer are due to units derived from 1-butene.
Ethylene-.alpha.-olefin copolymers of low molecular weight and containing residual double-bond unsaturation have been prepared using a new type of catalyst comprising a metallocene and an alumoxane, as disclosed in the following references.
U.S. Pat. No. 4,668,834 teaches ethylene-.alpha.-olefin copolymers and terpolymers having a M.sub.n of between about 250 and about 20,000, a viscosity index of at least about 75, and a vinylidene-type terminal unsaturation. The patent also discloses that the molar ethylene content of the copolymers is preferably in the range of between about 20 and about 80, more preferably between about 30 and about 70%, and most preferably between about 35 and about 65%. The patent further discloses the preparation of these polymers via certain Group IV catalysts, particularly certain metallocenes, and aluminoxane co-catalysts. Propylene and 1-butene are specifically disclosed to be among the preferred .alpha.-olefins for polymerization with ethylene. The ethylene-.alpha.-olefin copolymers and terpolymers are disclosed to be useful as intermediates in epoxy-grafted electrical encapsulation compositions. The patent contains examples directed to the preparation and epoxy-grafting of ethylene-propylene copolymers, but not of ethylene-1-butene (EB) copolymers. The use of these polymers to prepare ashless dispersants containing nitrogen is not disclosed.
U.S. Pat. No. 4,704,491 relates to liquid ethylene-.alpha.-olefin random copolymers, useful when hydrogenated as synthetic lubricant oil, characterized inter alia by having 10-85 mole % (=5-74 wt. %), preferably 20-80 mole % (=11-67 wt. %), most preferably 30-70 mole % (=17-54 wt. %) ethylene units; 15-90 (preferably 20-80, most preferably 30-70) mole % .alpha.-olefin units; M.sub.n of from 300 to 10,000; a M.sub.w /M.sub.n of not more than 2.5; and an iodine value in the range of 0 to 85. The copolymers are also characterized by a B value of at least 1.05 but not more than 2, wherein the B value is an index showing the state of distribution of monomer components in the copolymer chain and is defined as P.sub.OE /(2P.sub.O *P.sub.E), wherein P.sub.E is the molar fraction of ethylene component in the copolymer, P.sub.O is the molar fraction of the .alpha.-olefin component in the copolymer, and P.sub.OE is the molar fraction of .alpha.-olefin-ethylene chains in the total dyad chains. The patent discloses the B value may be determined from the C-13 NMR spectrum of the copolymer. The patent states that the liquid copolymer can be easily modified since it has a double bond capable of reacting with maleic anhydride, etc., at the molecular chain ends.
The patent further discloses that these copolymers can be produced by copolymerizing ethylene and a C.sub.3 -C.sub.20 .alpha.-olefin in the presence of a catalyst comprising a group IVb transition metal compound, such as a metallocene, and an aluminoxane. In addition to numerous examples directed to EP copolymers, the patent provides two examples of the preparation of EB copolymers by the polymerization of ethylene and 1-butene in the presence of zirconocene-aluminoxane catalyst systems. Example 6 discloses an EB copolymer having an ethylene content of 55 mole % (=38 weight percent) and an M.sub.n of 1200. Example 14 discloses an EB copolymer with 60 mole % ethylene (43 wt %) and M.sub.n of 2300.
PCT Published Application WO 90/1,503 is directed to ethylene-.alpha.-olefin polymers which have a molar content of ethylene of from about 20 to about 80 percent (=11-67 wt. %), preferably about 30 to about 70 percent (=17-54 wt. %), most preferably about 45 to about 65 percent (=29-48 wt. %); a number average molecular weight of from about 300 to about 10,000; and in which at least 90% of all polymer chains contain at least one carbon-carbon double bond and exhibit a ratio of vinylidene to vinyl double bonds of at least 3.5 to 1. It is disclosed that the polymers can be prepared by polymerization of ethylene and the .alpha.-olefin using certain metallocene-alumoxane catalysts and by using certain procedures and conditions. Example 5 discloses the preparation of an EB copolymer with M.sub.n of 860 using dimethylsilyldicyclopentadienyl zirconium dichloride and methylalumoxane. The remaining preparative examples are directed to EP copolymers.
U.S. Pat. No. 5,043,515 teaches a zirconocene/aluminoxane catalyst for oligomerizing olefins and the oligomerization process using the catalyst. More particularly, the patent discloses the oligomerization of ethylene or ethylene with one or more C.sub.3 -C.sub.10 .alpha.-olefins using the catalyst. It is further disclosed that, when the starting material is ethylene in combination with one or more .alpha.-olefins, the product olefins (i.e., the oligomers) contain significant portions of vinylidene olefins. Example 3-5 of the patent describes the oligomerization of ethylene and 1-butene using bis(cyclopentadienyl)zirconium dichloride and aluminoxane. The oligomers are disclosed to be useful as intermediates in preparing specialty detergents or lubricant additives.
The following references also disclose metallocene-alumoxane-prepared, low-molecular-weight ethylene-.alpha.-olefin copolymers, but are primarily directed to the chemical modification of the copolymers to provide additives for lubricating oils.
U.S. Pat. No. 4,981,605 relates to liquid epoxidized ethylenic random copolymers and to liquid hydroxylated ethylenic random copolymers, both of which are useful as lubricant oil additives, paint additives, and resin modifiers. The patent discloses that the epoxidized/hydroxylated ethylenic random copolymer is an epoxidation/hydroxylation product of a liquid ethylenic random copolymer of ethylene and a C.sub.3 -C.sub.20 .alpha.-lefin, wherein the epoxy/hydroxyl groups are each formed via a carbon-carbon unsaturated bond derived from ethylene or the .alpha.-olefin and positioned at the polymer chain end of the liquid ethylenic random copolymer. The patent further discloses that the liquid ethylene random copolymer has inter alia an ethylene component content of 10-85 mole %, an .alpha.-olefin content of 15 to 90 mole %, a M.sub.n of usually 200 to 10,000, and a molecular weight distribution of usually not more than 4.0. Referential Example 6 discloses the preparation of a liquid EB random copolymer with an ethylene content of 58 mole % (41 wt %) and M.sub.n of 1500 by polymerization of ethylene and 1-butene in the presence of bis(cyclopentadienyl) zirconium dichloride and aluminoxane.
European Published Patent Application 353,935 A1 is directed to oil-soluble lubricating oil additives comprising at least one terminally unsaturated ethylene-.alpha.-olefin polymer having a number average molecular weight of 300 to 10,000 substituted with mono- or dicarboxylic acid producing moieties, wherein at least about 30 percent of the polymer chains of the ethylene-.alpha.-olefin polymer possess terminal ethenylidene unsaturation. European Published Patent Application 441,548 A1 provides similar teachings for terminally unsaturated ethylene-.alpha.-olefin copolymers having number average molecular weights from about 300 to 20,000. EP 353,935 A1 further discloses that the monocarboxylic acid and the dicarboxylic acid or anhydride substituted polymers can be further reacted with a nucleophilic reagent such as amines, alcohols, amino alcohols and metal compounds, to form derivatives useful as lubricating oil additives such as dispersants. Suitable ethylene contents for the ethylene-.alpha.-olefin polymers are disclosed to range from 20 to 80, preferably 30 to 70, and most preferably 45 to 65 mole %. Example 5 discloses the preparation of an EB copolymer of M.sub.n of 860 using dimethylsilyldicyclopentadienyl zirconium dichloride and methylalumoxane. The ethylene content of the polymer is not disclosed in the Example. The subsequent functionalization of the polymer to an EB-substituted succinic anhydride (EBSA), and the derivatization of the EBSA with an amido amine are also exemplified.
U.S. Pat. No. 4,943,658 discloses liquid oxidatively modified ethylenic random copolymers, useful as formulating agents for lubricant oils, wherein the liquid ethylenic random copolymer comprises 20-80 mole % of ethylene and 80-20 mole % of .alpha.-olefin and has a number average molecular weight of from 200 to 10,000 and a molecular weight distribution in the range of up to 4. The examples are directed to the modification of EP copolymers.
U.S. Pat. No. 5,017,299 is directed to oil-soluble lubricating oil additives comprising Mannich Base condensates of an alkyl substituted hydroxy aromatic compound with formaldehyde and an amine, wherein the alkyl moiety of the aromatic compounds is derived from at least one ethylene-.alpha.-olefin copolymer of 300 to 10,000 number average molecular weight and wherein at least about 30% of the polymer chains contain terminal ethenylidene unsaturation.
While many of the above described metallocene-derived ethylene-.alpha.-olefin polymers can be successfully employed to make ashless dispersants, it has been found that further improvements in the performance of ashless dispersants incorporating such polymers, as well as significant improvements in the economics of the dispersants can be achieved by selectively controlling, for example, the monomer identity, monomer content, and certain polymer properties, within the broad general class of ethylene-.alpha.-olefin copolymers.